Dihybrid Cross: Phenotypic Ratio, Definition, Diagram and Overview

A dihybrid cross is a mating experiment that takes place between 2 individuals who are identical hybrids for two traits. In a dihybrid cross, the cross happens between the two traits that are under observation. The two genes of the traits under study are located on different pairs of homologous chromosomes and assort independently during gamete formation. The dihybrid cross-phenotypic ratio is 9:3:3:1.

Laws of Mendel

The father of modern genetics, “Gregor Mendel,” was the first person to discover the principle of heredity. He conducted various experiments, including one on pea plants in his garden, and he observed how the pattern of inheritance changed from one generation to the next.

His experiment on peas helped him to propose three of Mendel’s laws of inheritance, named as follows:

• Law of Segregation
• Law of Independent Assortment
• Law of Dominance

Also Read: Law of Segregation and Dominance

First, Mendel studied one gene in the plant using a monohybrid cross. In this, he only considered a single character, which was the height of the plant on a pair of peas with one contrasting trait. Next, he studied two genes in the plant using a dihybrid cross.

Characters with their Contrasting Traits

Mendel chose 7 contrasting characters for his hybridization experiments which are as follows –

What is a Dihybrid Cross?

A dihybrid cross is a breeding experiment between organisms with two contrasting traits. The individuals involved in this type of trait are homozygous for that specific trait. This experiment helps us in understanding how these traits are inherited independently in organisms. Genes are DNA segments that control these features.

Different pairs of alleles for each trait are carried by the parents in a dihybrid cross. While the other parent carries a homozygous recessive allele, one parent is homozygously dominant. All of the offspring born following the crossings in the F1 generation are heterozygous for particular traits.

Also Read: Dihybrid Cross Ratio

Dihybrid Cross Diagram

The visualisation of dihybrid cross using a Punnett square is given below –

Dihybrid Cross Example

Mendel crossed two features that were incompatible, such as the color and form of seeds, at a time. He crossed the spherical yellow seed and the green seed with wrinkles. In the F1 generation, he only succeeded in getting round yellow seeds. This demonstrated that seeds are often spherical and yellow.

In contrast, the seeds’ wrinkled shape and green color are distinct characteristics. F1 offspring were later self-pollinated. Four distinct seed combinations were produced as a result of the F2 generation. Within the phenotypic ratio is 9:3:3:1, there were wrinkled-yellow, round-yellow, wrinkled-green, and round-green seeds. He noticed a similar dominance and inheritance pattern during the monohybrid cross of these features. Hybridization also maintained the 3:1 phenotypic ratio of the round and wrinkled seed shape and the yellow and green seed color.

Consider the letters “Y” for seeds of yellow color, “g” for seeds of green color, “R” for seeds with a round shape, and “w” for seeds with a wrinkled shape. As a result, it is possible to deduce the parental genotype as “YYRR” (yellow-round seeds) and “yyrr” (green-wrinkled seeds).

Also Read: Difference Between Phenotype and Genotype Ratio

Conclusion – Dihybrid Cross

In conclusion, a dihybrid cross is a crucial genetic experiment that helps us understand how traits are inherited independently of each other. The dihybrid cross phenotype ratio is 9:3:3:1. By studying the offspring of individuals differing in two traits, we gain valuable insights into the patterns of inheritance for each trait separately. Through experiments like these, scientists continue to unravel the mysteries of genetics and advance our understanding of heredity.

Also Read:

• Difference Between Dihybrid and Monohybrid
• Monohybrid Cross – Inheritance of One Gene
• Heredity
• Incomplete Dominance
• Gregor Mendel and the Principles of Inheritance

FAQ’s – Dihybrid Cross

Who introduced the Dihybrid cross?

Gregor Mendel, the father of modern genetics, introduced dihybrid cross.

What is Mendel’s Dihybrid Cross Example?

The classic example of a dihybrid cross is Mendel’s pea experiment, in which the 2 traits of pea were crossed.

Why is a Dihybrid Cross called a Two-Trait Cross?

Because this crossing involves two organisms that are identical hybrids for two traits, a Dihybrid cross is also known as a two-trait cross.

Differentiate between Monohybrid and Dihybrid Cross.

In a dihybrid cross, two pairs of opposing traits are analyzed simultaneously, while in a monohybrid cross, only one trait is considered, involving parents that differ by a single trait

What is a 9:3:3:1 Dihybrid Cross?

 9:3:3:1 phenotypic ratio is a Mendelian ratio for a dihybrid cross where the alleles of two contrasting characters genes assort themselves independently of each other.